Fatigue crack growth (FCG) behaviour of 2.25Cr-1.0Mo steel plate and welds
tested in air and gaseous hydrogen was investigated. Microstructural observ
ations indicated that both the weld metal GYM) and heat-affected zone (HAZ)
were composed of mainly bainitic microstructure. A ferrite matrix with uni
formly dispersed carbides was found in the annealed base metal. The change
in microstructures of WM and HAZ between the as-welded and tempered welds w
as limited. The as-welded WM had the lowest impact toughness among the spec
imens, however, the impact toughness was improved after postweld heat treat
ment at 700 degreesC/1 h. Regardless of the testing environments, the as-we
lded WM exhibited a higher resistance to crack growth than the steel plate
as the crack propagated transversely to the welding direction, especially i
n the low DeltaK range. However, higher fatigue crack growth rates in the a
s-welded HAZ than those of the steel plate were found. As the crack grew al
ong the fine-grained heat-affected zone in the as-welded condition, signifi
cant retardation of crack growth as compared with that of the steel plate w
as obtained when tested in air or gaseous hydrogen. In various regions of t
he weld, the FCG behaviour of tempered welds was similar to that of the ste
el plate in air. The results also indicated that the tempered bainitic micr
ostructure present in WM or HAZ was more resistant to unstable crack growth
than the annealed steel plate tested in gaseous hydrogen. Environmentally
induced acceleration of FCG in various regions of the weld was usually exhi
bited a change of fracture features. (C) 2001 Elsevier Science B.V. All rig
hts reserved.